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.\" $Id: curs_variables.3x,v 1.49 2024/06/22 21:25:23 tom Exp $
.TH curs_variables 3X 2024-06-22 "ncurses 6.5" "Library calls"
.ie \n(.g \{\
.ds `` \(lq
.ds '' \(rq
.\}
.el \{\
.ie t .ds `` ``
.el   .ds `` ""
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.
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.de bP
.ie n  .IP \(bu 4
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..
.
.SH NAME
\fI\%bool\fP,
\fI\%chtype\fP,
\fI\%cchar_t\fP,
\fI\%attr_t\fP,
\fI\%SCREEN\fP,
\fI\%WINDOW\fP,
\fB\%TRUE\fP,
\fB\%FALSE\fP,
\fB\%ERR\fP,
\fB\%OK\fP,
\fB\%curscr\fP,
\fB\%newscr\fP,
\fB\%stdscr\fP,
\fB\%COLORS\fP,
\fB\%COLOR_PAIRS\fP,
\fB\%COLS\fP,
\fB\%LINES\fP,
\fB\%ESCDELAY\fP,
\fB\%TABSIZE\fP \-
\fIcurses\fR data types, constants, and global variables
.SH SYNOPSIS
.nf
\fB#include <curses.h>
.PP
\fI/* data types */
\fBtypedef \fI/*\fP .\|.\|. \fI*/\fP bool;
\fBtypedef \fI/*\fP .\|.\|. \fI*/\fP chtype;
\fBtypedef \fI/*\fP .\|.\|. \fI*/\fP cchar_t;
\fBtypedef \fI/*\fP .\|.\|. \fI*/\fP attr_t;
\fBtypedef \fI/*\fP .\|.\|. \fI*/\fP SCREEN;
\fBtypedef \fI/*\fP .\|.\|. \fI*/\fP WINDOW;
.PP
\fI/* constants */
\fBconst bool TRUE;
\fBconst bool FALSE;
.PP
\fBconst \fI/*\fP .\|.\|. \fI*/\fP ERR;
\fBconst \fI/*\fP .\|.\|. \fI*/\fP OK;
.PP
\fI/* variables */
\fBint COLORS;
\fBint COLOR_PAIRS;
\fBint COLS;
\fBint LINES;
\fBWINDOW * curscr;
\fBWINDOW * stdscr;
.PP
\fI/* extensions */
\fBint ESCDELAY;
\fBint TABSIZE;
\fBWINDOW * newscr;
.fi
.SH DESCRIPTION
This page summarizes data types,
constants,
and variables provided by the \fIcurses\fP library.
Locate further discussion in \fB\%curses\fP(3X).
.PP
Depending on \fI\%ncurses\fP's build-time configuration,
the variables may instead be
macros (see \fB\%curs_threads\fP(3X) and \fB\%curs_opaque\fP(3X))
that provide read-only access to the library's state.
In either case,
applications should treat them as read-only to avoid
confusing the library.
.SH "CONSTANTS"
.SS "TRUE, FALSE"
The \fIcurses\fP library defines \fBTRUE\fP and \fBFALSE\fP
to represent the values of the Boolean data type.
.SS "ERR, OK"
\fIcurses\fP and \fIterminfo\fP routines frequently return these
constant integral values indicating failure and success,
respectively.
.SH "PREDEFINED TYPES"
.SS "\fIbool\fP"
X/Open Issue 4 \fIcurses\fP (1996) preceded the ISO C99 and ISO C++98
standards,
each of which also defined a Boolean data type.
The \fIcurses\fP library requires an integral type \fIbool\fP.
.PP
\fB\%ncurses\fP' configure script attempts to discover the
data type used by the system's C and C++ compilers,
to reuse for the \fIcurses\fP \fIbool\fP.
.SS "\fIchtype\fP"
The \fI\%chtype\fP integral type combines a
(\*(``narrow\*('',
8-bit)
character with attributes encoding the character's \fIrendition\fP,
such as the styling of its typeface and/or foreground and background
colors.
See,
for example,
\fB\%addch\fP(3X),
\fB\%attron\fP(3X),
and
\fB\%inch\fP(3X).
.SS "\fIcchar_t\fP, \fIattr_t\fP"
\fI\%chtype\fP is too small for the standard C library's wide-character
type,
\fIwchar_t\fP.
\fI\%cchar_t\fP is a type that can accommodate an \fI\%attr_t\fP and
enough wide characters to store what Unicode terms a \fIgrapheme cluster\fP
(a \*(``user-perceived character\*('' [UAX #29],
which may nevertheless require several character encoding units to
represent).
\fI\%attr_t\fP is an integral type storing \*(``wide\*('' attributes that
apply to \fI\%cchar_t\fPs.
See,
for example,
\fB\%add_wch\fP(3X),
\fB\%attr_on\fP(3X),
and
\fB\%in_wch\fP(3X).
.SS "\fISCREEN\fP"
.I curses
manages a terminal device with this structure type;
see \fB\%initscr\fP(3X).
.SS "\fIWINDOW\fP"
.I curses
represents rectangular portions of the terminal screen with the
.I \%WINDOW
structure type;
see subsection \*(``Overview\*('' of \fB\%ncurses\fP(3X).
.SH "VARIABLES"
.SS "curscr, stdscr, newscr"
The library records updates to the terminal screen in a window named
\fB\%curscr\fP.
This object is referred to as the \*(``physical screen\*('' in
\fB\%curs_refresh\fP(3X) and
\fB\%curs_outopts\fP(3X).
.PP
\fI\%ncurses\fP collects pending updates to the terminal screen in a
window named \fB\%newscr\fP.
This object is referred to as the \*(``virtual screen\*('' in the
\fB\%curs_kernel\fP(3X),
\fB\%curs_refresh\fP(3X),
and
\fB\%curs_outopts\fP(3X).
When the screen is refreshed,
\fIcurses\fP determines a minimal set of updates using the terminal's
capabilities to make \fB\%curscr\fP look like \fB\%newscr\fP.
.PP
Once \fIcurses\fP is initialized,
it creates a window named \fB\%stdscr\fP.
It is the same size as the terminal screen and is the default window
used by routines that do not take a parameter identifying one.
Many \fIcurses\fP functions use this window.
.SS COLORS
Once \fIcurses\fP is initialized,
\fB\%COLORS\fP
contains the number of colors supported by the terminal;
see \fB\%curs_color\fP(3X).
.SS COLOR_PAIRS
Once \fIcurses\fP is initialized,
\fB\%COLOR_PAIRS\fP
contains the number of color pairs supported by the terminal;
see \fB\%curs_color\fP(3X).
.SS "COLS, LINES"
Once \fIcurses\fP is initialized,
.B \%COLS
and
.B LINES
contain the screen's width and height in character cells,
respectively;
that is,
the number of columns and lines.
.SS ESCDELAY
For
.I curses
to distinguish the ESC character resulting from a user's press of the
\*(``Escape\*('' key on the input device from one beginning an
.I "escape sequence"
(as commonly produced by function keys),
it waits after the escape character to see if further characters are
available on the input stream within a short interval.
.B \%ESCDELAY
stores this interval in milliseconds.
.PP
If \fB\%keypad\fP(3X) is disabled for the
.I curses
window receiving input,
a program must disambiguate escape sequences itself.
.SS TABSIZE
The \fIcurses\fP library converts a tab character to this number of
spaces as it adds a tab to a window;
see \fB\%curs_addch\fP(3X).
.SH NOTES
Either \fB\%initscr\fP(3X) or \fB\%newterm\fP(3X) initializes
\fIcurses\fP.
.PP
If
.I \%ncurses
is configured to provide separate
.I curses
and
.I \%tinfo
libraries,
most of these variables reside in the former.
.SH PORTABILITY
The X/Open Curses standard documents all of the foregoing types and
symbols except for \fB\%newscr\fP,
\fB\%TABSIZE\fP,
and \fB\%ESCDELAY\fP.
.PP
X/Open Curses describes \fB\%curscr\fP only as \*(``an internal data
structure\*('';
SVr4 gave more details,
noting its use \*(``for certain low-level operations like clearing and
redrawing a screen containing garbage\*(''.
.\" SVID 4, Volume 3, p. 408
Neither specified its interaction with the rest of the interface beyond
use as an argument to \fB\%clearok\fP(3X) and \fB\%wrefresh\fP(3X).
.PP
\fB\%newscr\fP is a feature of SVr4 \fIcurses\fP.
When refreshing the screen,
it is used as a working area for combining the standard window
\fB\%stdscr\fP with any others the application may have created with
\fB\%newwin\fP(3X).
When the update of \fB\%newscr\fP is complete,
\fIcurses\fP modifies \fB\%curscr\fP to match \fB\%newscr\fP.
.PP
\fB\%TABSIZE\fP is a feature of SVr4 \fIcurses\fP.
.bP
SVr4 initially sets \fB\%TABSIZE\fP from the terminal description's
\fB\%init_tabs\fP capability.
After that,
it can be altered by applications using SVr4 \fIcurses\fP.
.bP
SVr4 \fIcurses\fP uses the value of \fB\%TABSIZE\fP to compute the
position of tab stops when updating both
the virtual screen with \fB\%addch\fP(3X) and
the physical screen with \fB\%mvcur\fP(3X).
.bP
\fI\%ncurses\fP uses the value of \fB\%TABSIZE\fP only to update the
virtual screen.
It uses the terminal description's \*(``\fBit\fP\*(''
\%(\fBinit_tabs\fP) capability for computing hardware tabs
(that is,
tab stops on the physical screen).
.bP
Other implementations differ.
For instance,
NetBSD \fIcurses\fP allows \fB\%TABSIZE\fP to be set through an
environment variable.
\fI\%ncurses\fP does not.
.IP
NetBSD \fIcurses\fP does not support hardware tabs;
it uses the \fB\%init_tabs\fP capability and the \fB\%TABSIZE\fP
variable only for updating the virtual screen.
.PP
\fB\%ESCDELAY\fP is a feature of AIX \fIcurses\fP.
.bP
In AIX,
the units for \fB\%ESCDELAY\fP are \fIfifths\fP of milliseconds.
.bP
The default value for AIX's \fB\%ESCDELAY\fP equals 0.1 seconds.
.bP
AIX also enforces a limit of 10,000 seconds for \fB\%ESCDELAY\fP;
\fI\%ncurses\fP does not enforce any upper limit.
.PP
\fI\%ncurses\fP has long used \fB\%ESCDELAY\fP with units of
milliseconds,
making it impossible to be completely compatible with AIX.
Consequently,
most users have decided either to override the value,
or to rely upon its default.
.SH SEE ALSO
\fB\%curses\fP(3X),
\fB\%curs_color\fP(3X),
\fB\%curs_opaque\fP(3X),
\fB\%curs_terminfo\fP(3X),
\fB\%curs_threads\fP(3X),
\fB\%term_variables\fP(3X),
\fB\%terminfo\fP(5)
.PP
[UAX #29] \*(``Unicode Standard Annex #29: Unicode Text
Segmentation\*('';
\%<https://\*:unicode\*:.org/\*:reports/\*:tr29/>
